The present invention relates to data storage technology in a computer system and, more particularly, to a combined volatile and nonvolatile memory device formed on the same semiconductor substrate, and an interface therefor.
As the speed and capabilities of electronic devices continue to increase, so must the speed and capability of the memory components that support these devices. For example, in the past, computer systems, such as personal computers, telephones, fax machines, audio, video, and other electronic devices, were primarily stationary in nature, and were primarily supplied power through a local wall outlet. Today, however, and more increasingly in the future, many of these devices have become more miniaturized, and are supplied power from an internal battery, enabling these devices to enter the mobile market. This trend toward miniaturization and low-power battery operation necessarily extends to all aspects of these devices, including their electronic memory components.
As a specific example, consider the mobile cellular telephone. Market forces work to continually reduce the size of the cell phone while demanding increased capability. Early mobile phones weighed in excess of ten pounds and were the size of a briefcase. These phones did nothing more than allow a user to dial a number and communicate with a second party. Today, the weight of cellular phones is measured in ounces rather than pounds, and these phones incorporate advanced features such as, for example, name and number storage and security. In the near future, cellular phones will take on more personal digital assistant (PDA) features such as, for example, faxing, computing, internet access, messaging, scheduling, and handwriting and voice recognition.
To be marketable, each of these features will require more advanced memory technologies than what is currently available. The memory components that will support future mobile electronic devices need to have a large memory capacity, be quickly accessible, operate at low power, and maintain the integrity of stored data through power fluctuations, such as would occur when the battery is removed or its supply to the electronic device is otherwise interrupted.
One type of data storage medium is generically referred to as random access memory (RAM). Specific types of RAM include, for example, dynamic RAM (DRAM), static RAM (SRAM), video RAM (VRAM), and synchronous DRAM (SDRAM). These and other types of RAM storage devices share some common attributes. For example, data can be read from or written to locations in a RAM array relatively quickly in comparison to other types of memory devices. In addition, manufacturing process technology has evolved to enable RAM devices, such as DRAM, to be formed in high densities using specialized techniques. Unfortunately, RAM devices belong to a class of memory devices called volatile memory, meaning that the data stored in a RAM array is erased as soon as the power supply to the array is removed. Therefore, to maintain the integrity of data stored in a RAM array, power to the array must be maintained at all times. Unfortunately, this condition cannot be readily satisfied in mobile electronic devices, making volatile memory components such as RAM devices ill-suited for mobile applications in which data is required to be stored for extended periods of time.
Another type of memory device is known as read-only memory (ROM). This type of memory belongs to a class of memory devices called non-volatile memory because data stored in a ROM array is permanently fixed in the array until the array is intentionally erased. Even if the power supplied to the memory array of a ROM device is entirely removed, the data stored within the array is still maintained. Some common types of ROM memory devices include programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), and flash memory.
Data can be very quickly read from a flash memory device, nearly as fast or faster than the same data can be read from a RAM device. In addition, highly specialized manufacturing process technologies have been developed that enable high density flash arrays to be formed on a semiconductor substrate. For these reasons, flash memory devices are well suited for incorporation into mobile electronic devices for long-term storage of data. Unfortunately, it takes a long period of time to write data to a flash memory array. For example, it is not uncommon for it to take well over a thousand times as long to write data to a flash array as it does to read that data back out of the flash array. Moreover, erasing a particular block within the flash array before writing data to the block represents an even greater time delay.
One desire of the present invention is to provide a memory device for a computer system that supports fast read and write capability.
Another desire of the invention is to provide a memory device for a computer system that stores data in a nonvolatile manner.
An integrated circuit memory device comprising both volatile and nonvolatile memory arrays formed on a single semiconductor substrate is described. An interface is provided to couple the volatile memory array to the nonvolatile memory array. The interface is configured to write data to the volatile memory array, and to subsequently write that data from the volatile memory array to the nonvolatile memory array.